I'm not familiar with this amp but if these are mono amps and they each have 4 binding posts, the likely answer is that there are three impedance settings supported. If like most Decware amps nothing is marked, the black post will be for the negative speaker wire. The other three will be (I'm guessing) for 4 ohm, 8 ohm, and 16 ohm speakers and would connect the positive speaker wire. Only one of these three will be used. I would try each one however to see which one sounds the best regardless of how your speakers are rated, just make sure both channels are connected the same.

Edit: Just saw the pictures on the other forum. I was wrong and now I can't offer a guess. Never mind. :)